The roofs, floors and other parts of many buildings and structures are constructed with prefabricated trusses made of wood or similar materials. Such type of trusses are typically constructed using cord members that define the basic outline and shape of the truss, and using internal interconnecting web members to provide structural integrity and strength to the overall truss. In this manner, the trusses need not be made of a solid material, but can nevertheless withstand significant loads spanning between end points such as walls or foundations. Although, trusses can be constructed of metal framework members, the cost and weight can be significant. A wide variety of wood trusses are nevertheless available, due primarily to the lower cost than that of metal trusses. The cost of wooden trusses is lower due primarily to the lower cost of lumber, and such trusses are less labor intensive to fabricate. Much of the construction and fabrication of wooden trusses has been automated to reduce the manual labor involved, especially the assembling and fastening together of the truss members at the joints to form a rigid and integral unit. Currently, the structural cord and web members of a truss are fastened together by nail plates placed on opposite sides of the joint, and pressed together so as to be embedded in the wood to permanently fix the truss members together at the joint.
FIG. 1 illustrates a table or jig 10 typically used for fabricating a truss 12. The truss 12 includes cord members 14, 16 and 18, with the internal web members 20-28 to provide structural integrity to the truss. The table 10 is supported above a floor by legs, standoffs, or the like. While not shown, the top of the table 10 has a number of slots or holes for the insertion of pegs to define the size and outline of the truss. The jig is arranged so that the parts of the truss can be laid out in a prearranged manner on the table 10, with nail plates, such as 30, disposed above and below each truss joint. As can be appreciated, each different truss 12 requires a different jig or pattern to arrange the wooden parts of the truss thereon. Once the truss parts are arranged on the table 10 with the nail plates 30 on each side of the respective joints, a gantry roller 32 is moved along the table 10 by way of a rail arrangement 34, thereby squeezing the truss 12 between the table and the roller 32. The gantry rollers and truss tables are shown in more detail in U.S. Pat. Nos. 3,464,348; 3,538,843; 3,855,917 and 5,211,108, the disclosures of which are incorporated herein by reference.
FIG. 2 illustrates in more detail a joint 36 of a truss 12 having cord members 14 and 16 butted together at the ends thereof. A top nail plate 38 and a bottom nail plate 40 are placed on each side of the truss joint 36. The gantry roller 32 is then rolled to the right over the truss, as shown in FIG. 2, to thereby partially embed the sharp projections 42 of the nail plates into the truss members 14 and 16. The purpose of the gantry roller 32 is to only partially embed the nail plates into the wood to make a more rigid and unitary structure for further processing.
Once the gantry roller 32 has passed over the truss 12 and has partially embedded the nail plates 38 into the wood members, the truss is processed by a pair of downstream finish rollers which completely embed the nail plates into the wooden truss members. As a result of the foregoing truss fabricating steps, an undesired bow, bend or camber results, as shown in FIG. 3. The bow is inadvertently formed in the truss joints because the gantry roller 32 does not apply a uniform pressure to all parts of the top nail plate 38, whereas the table 10 does apply a uniform pressure to the entire surface area of the bottom nail plate 40. The undesirable bow formed at a truss joint is generally in a direction shown in FIG. 3, where the truss members that extend away from the joint are bowed upwardly. It can be appreciated that a slight bow is generally formed at each truss joint 36, and the extent of the overall bow of the entire truss becomes cumulative with the number of joints involved. In other words, as the truss becomes longer, and thus involves more joints and larger nail plates, the overall bow of the truss tends to become excessive.
As noted above, after the truss 12 has been fastened together by the incomplete embedding of the nail plates into the truss joints, the entire truss itself is moved to a powered roller conveyor where the truss is carried to a pair of finish rollers, which are not shown in FIGS. 1-3. The finish rollers are essentially a pair of vertically spaced-apart rollers that receive the leading end of the truss to pull it between the rollers and completely embed the nail plates into the wood truss members. To that end, the spacing between the finish rollers is somewhat less than the thickness of the wood truss members, thereby assuring that the nail plates will be completely pressed into the wood truss members. Experience has shown that the finish rollers do not remove the bow at the truss joints, and thus the completed truss still includes an inherent bow at the joints thereof. The bow at each truss joint is not only unsightly, but it can be both structurally unsound and troublesome in fastening other structural components thereto, such as wood cross pieces to tie a number of truss members together.
It can be seen from the foregoing that an inherent problem exists in the formation of wooden trusses with the members attached together by nail plates, and where a gantry roller, or the like, is utilized to partially embed the nail plates to the truss members. A need therefore exists for a technique for removing the bow at each truss joint to thereby straighten the truss. A further need exists for a technique to straighten trusses of the type described without significantly altering the established prefabrications techniques or equipment. A further need exists for truss straightening equipment that is cost effective, easily installed in existing assembly lines, and is reliable and trouble free.